Fuel-air mixture apparatus

ABSTRACT

In a fuel-air mixture device, downstream of a throttle ( 4 ) and a fuel introduction device, a block ( 51 ) is provided across the primary air passage ( 2 ). The block has a plurality of passageways ( 54 ) through it for air flow towards an inlet manifold. These improve mixture of the fuel and air.

BACKGROUND OF THE INVENTION

The present invention relates to a fuel-air mixture apparatus,particularly for an internal combustion engine.

Fuel-air mixture apparatuses of the type where fuel is mixed with airprior to induction into the cylinder(s) of an engine generally rely on apressure reduction at a throttle in the device to draw fuel into thedevice, in which case the device is known as a carburettor, or rely onfuel injection into the air as it passes through the device.

Generally, the prior devices rely on a single stage of mixture of fueland air and are limited as regards the droplet size and totalvaporisation of the fuel in the air which they induce. Inadequatevaporisation and too large a droplet size result in unburned and/orincompletely burnt fuel being present in the exhaust from the engine.

In my International Application No WO 97/48897, I have described andclaimed an invention which I refer to below as “My Earlier Invention”and which comprises a fuel-air mixture apparatus having:

a primary air passage having an inlet, an adjustable throttle and anoutlet,

a secondary air passage having an inlet and an outlet to the primary airpassage between its adjustable throttle and its outlet,

a variable orifice nozzle for introducing fuel into the secondary airpassage, the nozzle having a mouth and a down-stream pointing taperedneedle in the mouth to provide variability of the orifice by axialmovement of the needle and

a linkage or control device for linking or controlling the position ofthe needle to the position of the adjustable throttle in the primary airpassage for adjustment of the orifice of the nozzle,

the arrangement being such that in use the fuel mixes with the airflowing through the secondary air passage prior to mixing with the airflowing in the primary air passage and the fuel flow from the nozzle ismatched to the position of the adjustable throttle.

THE INVENTION

The object of the present invention is to a further improved fuel airmixture apparatus.

The invention is based on passing a fuel-air mixture through anapertured vaporisation block in the apparatus to enhance the degree ofmixing of the fuel with the air.

According to my present invention, there is provided a fuel-air mixturedevice comprising:

a primary air passage having an inlet, an adjustable throttle and anoutlet,

a variable orifice nozzle for introducing fuel to the primary airpassage, the nozzle having a mouth and a tapered needle in the mouth toprovide variability of the orifice by axial movement of the needle, theneedle being arranged transversely of the primary air passage and

a linkage or control device for linking or controlling the position ofthe needle to the position of the adjustable throttle in the primary airpassage for adjustment of the orifice of the nozzle and

an apertured vaporisation block having a plurality of air passagewaysthrough the block, which subdivide a portion of the primary air passagebetween the fuel introduction position and the outlet.

The apertured vaporisation block may be integral with a member definingthe primary air passage. Alternatively it may be fitted to the latter.In this case, the apertured vaporisation block may be mounted in suchmanner as to be ultrasonically excitable. Typically this can be bymounting the block in an ultrasonically excitable ring. Alternatively,the passageways in the block can be lined by ultrasonically excitabletubes.

The apertured vaporisation block can be a solid block in which the airpassageways are formed by machining or casting. Alternatively, theapertured vaporisation block can be laid up from a plurality of layers,preferably by winding, the layers having regular formations extendingout from each layer to space it from the next layer. The formations ateach layer can be continuous with the formations at the next orinter-spaced with the formations at the next.

In one preferred embodiment, the apertured vaporisation block isprovided wholly downstream of the position of the fuel introductionmeans, preferably with an upstream face of the apertured vaporisationblock being formed concavely, preferably conically.

In another preferred embodiment, the apertured vaporisation block isprovided at and extending downstream of the position of the fuelintroduction means.

Whilst I envisage the contrary, I prefer that the present fuel-airmixture apparatus should be fully in accordance with My EarlierInvention, that is to say incorporating:

a secondary air passage having an inlet and an outlet to the primary airpassage between its adjustable throttle and its outlet,

the arrangement being such that in use the fuel mixes with the airflowing through the secondary air passage prior to mixing with the airflowing in the primary air passage and the fuel flow from the nozzle ismatched to the position of the adjustable throttle.

In the embodiment wherein the apertured vaporisation block is providedat and extending downstream of the position of the fuel introductionmeans, the apertured vaporisation block has at least one transverse boreleading from the secondary air passage to a respective one of the airpassageways through the block. Each of the passageways can have atransverse bore leading from the secondary air passage. Alternatively,some of the air passageways may not be in communication with thesecondary air passage and not receiving fuel-air mixture in use. Some ofthe air passageways may be in communication with the secondary airpassage only via others of them.

The fuel introduction needle may extend into one or more of the airpassageways in the apertured vaporisation block.

It is envisaged that the passageway(s) having the transverse bore(s) canbe configured as venturi(s) with the narrowest throat(s) being at theorifice(s) of the transverse bore.

To aid mixture of the fuel with the air in the passageways, the lattercan have turbulence inducing formations downstream of the transversebore.

To help understanding of the invention, a specific embodiment thereofwill now be described by way of example and with reference to theaccompanying drawing, in which:

FIG. 1 is a cross-sectional side view of a fuel-air mixture apparatus ofthe invention;

FIG. 2 is a scrap cross-sectional view on a larger scale of the needleactuator in the apparatus of FIG. 1 with the needle in its closedposition;

FIG. 3 is a similar view of the actuator with the needle in its openposition;

FIG. 4 is a similar view of an alternative air passageway block;

FIG. 5 is a view similar to FIG. 1 of an alternative apparatus of theinvention;

FIG. 6 is a cross-sectional end view of the air passageway block in theapparatus of FIG. 5;

FIG. 7 is an end and perspective view of another alternative airpassageway block; and

FIG. 8 is a similar pairs of views of yet another air passageway block.

The fuel-air mixture device shown in FIG. 1 is a carburettor. It has anair passage member 1 defining a primary air passage 2 with an inlet 3,an adjustable throttle 4 and an outlet 5. The inlet will be connected inuse to an air cleaner (not shown), the outlet will be connected to anengine manifold (not shown) and the throttle will be connected to athrottle control (also not shown). The throttle has a vane 6 carried ona shaft 7 journalled in a body 8—into which the air passage member 1 isfitted—and having at one end a cam plate 9 against which a needleactuator 10 bears.

Referring additionally to FIGS. 2 & 3, the needle actuator is slidinglyaccommodated in a needle carrier 11 fitted into a bore 12 in the body 8and sealed there by a pair of O-rings 13. The needle carrier is retainedby a flange 14 against which a block 15 acts, the block being held inplace by the throttle shaft 7. Between the O-rings 13, the needlecarrier has a circumferential groove 16, which opens to the interior 17of the needle carrier 11. A fuel supply duct 18 in the body communicateswith a fuel supply line 19 and the groove 16. The interior of the needlecarrier is defined by a bore 20 in which the needle actuator 10 isaccommodated in a fuel tight manner, with a seal 21 in a groove at thebottom end of the actuator. A spring 22 in a lubricant chamber 23 actsbeneath a flange 24 on the needle actuator and urges the latter via anend dome 25 against a rotary cam surface 26 of the cam plate 9. A needle27 is carried axially of the needle carrier in a bore 28 in the needleactuator 10. The needle has a head 29 accommodated in the actuator. Aspring 30 captivated by the dome 25 urges the needle 27 towards theprimary air passage 2. A seal 31 on the needle seals it to its actuator10. A shank 32 of the needle extends from the actuator and has at itopposite end a groove carrying an O-ring 33 and a steep taper 34, whichcan seat in an internal orifice 35 in the needle carrier 11, with theO-ring 33 seating just outside the orifice (see FIG. 2), when the needleactuator is displaced so far by the cam as cause the head 29 and/or theseal 31 to lift from and abutment 36 in the carrier on which it normallyengages, as shown in FIG. 2.

In the normal operating position of the cam plate 9, as shown in FIG. 3,with the needle actuator lifted by the spring 22, the needle head 29,seal 31 and abutment 36 are held together and the taper 34 is drawnclear of the orifice 35. The needle has a finely tapered needle proper37 extending on through the orifice from the thin end of the steeptaper, for varying the extent to which the orifice is open to thepassage of fuel in accordance with the longitudinal position of theneedle. This position is directly linked to the position of the throttleby the cam.

The needle terminates in a “pip” 38, which encourages any fuel runningalong its fine taper to shed as a fine droplets.

Beyond the orifice 315 of the needle carrier 11, it has an extension 39having two external grooves 40,41, from which lead bores 42,43 to anoutwardly tapering mouth 44 of the carrier. This is in register with asimilarly tapering opening 45 in the air passage member 1, opening intothe primary air passage 2.

A secondary air passage 46 leads from the primary air passage 2 upstreamof the throttle 4. The passage 46 branches into two 47,48. The smaller47 of these leads via a slow running, secondary air flow adjustment 49to the upper groove 40, whose bores 42 open to the narrow end of thetapered mouth 44. The larger secondary air branch 48 intercepts the bore49 in which the throttle shaft 7 is journalled. At the interception. theshaft has a flat 50, which aligns with the branch when the throttle isopen, but closes the branch when the throttle is closed for slow runningwhereby the secondary air all passes via the other branch. The largerbranches opens into the groove 41, via which its air passes on to thebores 43 and into the mouth 44 for mixing with the fuel metered by theneedle.

Down-stream of the mouth 44, a block 51 is provided across the primaryair passage 2. It is mounted in a ring 52 of piezoelectric materialprovided with an excitation circuit 53. The block has a plurality ofpassageways 54 through it for air flow towards the inlet manifold. Theseincrease the turbulence in the air flow and increase the surface area onwhich fuel can deposit as fine droplets during the periods of stagnationcorresponding to compression, ignition and exhaust for a single cylinderengine.

In operation of the carburettor, the throttle is opened. This allows theneedle to move back from its position closing the orifice 34. Fuel,generally petrol, is allowed to flow at a rate appropriate to thethrottle opening. It enters the mouth 44 and mixes with the secondaryair flow. This air and the fuel, which represent a richandnon-homogeneous mixture, flows on to the primary air passage. Heremixture of the fuel and air reaches the desired composition. On enteringthe passageways 54, the homogeneity is improved by turbulence in thepassageways and by the provision of a large surface area on which fuelcan deposit during stagnation and be reevaporated during air flow.Further turbulence occurs on exit from the passageways.

FIG. 4 shows an alternative construction of the block 51′, in which thering 52 is dispensed with and replaced by a series of piezoelectrictubes 55, which are all excitable. This block also has a conically,concave upstream face 56, which encourages laminar flow in the tubes 55.In a further, simpler alternative, the piezoelectric elements can bedispensed with as in the following embodiment.

Turning now to FIGS. 5 & 6, the carburettor there shown is essentiallysimilar to that of FIGS. 1, 2 & 3, except that the block 151 ispositioned to receive the secondary air flow directly into itspassageways 154. In place of the mouth 44. the air passage member 101has a V-slot 144 cut in it, to spread partially around the block. Theblock has a number of bores 160 opening from the slot 144 to convey theflow of secondary air and fuel to some of the passageways 1541. Others1542 do not receive secondary airflow. The fuel is mixed with airflowing in these downstream of the block 151 due to turbulence in theair streams leaving the passageways.

A number of variants can be envisaged. The needle may extend into one ofthe radial bores aligned with the needle. As shown the passageways 154are parallel bores. At least those 1541 into which the radial bores leadmay be formed with venturis at the junction with these bores toencourage the secondary air flow into them. Further downstream of thebores, the passageways may be provided with surface roughness to promoteturbulent air flow and mixture of the fuel and air flowing in them.

Whilst the apertured vaporisation blocks 51, 51′, 151 are solid blocksin which the passageways are formed by machining or casting, thealternatives 251,351 shown in FIGS. 6 & 7 formed of a plurality oflayers 2511, 3511. These are of sheet metal and spirally wound. Thelayers 2511 have a series of spacers 2512, which are two thicknesses ofthe sheet metal abutted and adhered together to form the spacers with aheight equal to the spacing of the layers. The spacers are aligned togive structure rigidity. The layers 3511 have similar spacers 3512, butwhich are not abutted, and meet the next layer at peaks 3513, which areadhered to the next layer. The spacers can be angled with respect to thedirection of their spiral winding, to give airflow through the block avortex flow. As an alternative to the spacers being wound, they could becast or moulded.

The invention is not intended to be restricted to the details of theabove described embodiment. Various alternatives have been identified inthe description above just before the description of the drawing. Inaddition, the passageways may be provided in a variety of sizes. As inmy earlier invention, the direct mechanical linkage between the positionof the needle and the position of the throttle can be replaced byelectronic control.

What is claimed is:
 1. A fuel-air mixture device comprising: a primaryair passage having an inlet, an adjustable throttle mounted on a rotaryshaft arranged transversely of said primary air passage and an outlet; asecondary air passage having an inlet from said primary air passagebetween its inlet and its adjustable throttle and an outlet to saidprimary air passage between its adjustable throttle and its outlet; avariable orifice nozzle for introducing fuel to said primary airpassage, said nozzle having a mouth for dispensing fuel into saidsecondary air passage upstream of its outlet; a tapered needle arrangedradially of said primary air passage and positioned in said mouth toprovide variability of said orifice by axial movement of said needle,said needle being arranged transversely of said primary air passage withits small diameter end directed towards said primary air passage, thearrangement being such that in use, said fuel mixes with air flowingthrough said secondary air passage prior to mixing with air flowing insaid primary air passage; a linkage mechanism for controlling theposition of said needle to the position of said adjustable throttle insaid primary air passage for adjustment of said orifice of said nozzle;an actuator for said tapered needle acted on by said linkage, with saidneedle extending between said actuator and said fuel dispensing mouth ofsaid nozzle, the arrangement being such that as said throttle is opened,said needle is moved away from said primary air passage and out of saidmouth of said nozzle to match fuel flow from said nozzle to saidposition of said adjustable throttle; and an apertured vaporisationblock having a plurality of air passageways through said block, whichsubdivide a longitudinal portion of said primary air passage betweensaid fuel introduction position and said outlet, the arrangement beingsuch that fuel, air flowing through the secondary air passage and airflowing through said primary air passage all pass through said airpassages for mixture of the fuel and the air; and wherein said linkagemaintains a cam plate carried on said transverse, throttle-carryingshaft and having a cam surface directed towards said primary airpassage, with said actuator for said tapered needle bearing against saidcam plate.
 2. A fuel-air mixture device according to claim 1, includinga spring for lifting said needle from said mouth of said nozzle, undercontrol of said cam plate, as said throttle is opened.
 3. A fuel-airmixture device according to claim 1, wherein said apertured vaporisationblock is integral with a member defining said primary air passage.
 4. Afuel-air mixture device according to claim 1, wherein said aperturedvaporisation block is a member fitted to said primary air passage.
 5. Afuel-air mixture device according to claim 4, wherein said aperturedvaporization block is mounted in such manner as to be ultrasonicallyexcitable.
 6. A fuel-air mixture device according to claim 5, whereinsaid apertured vaporisation block is mounted in an ultrasonicallyexcitable ring.
 7. A fuel-air mixture device according to claim 5,wherein said passageways in said block are lined by ultrasonicallyexcitable tubes.
 8. A fuel-air mixture device according to claim 1,wherein said apertured vaporisation block is a solid block in which saidair passageways are formed by machining or casting.
 9. A fuel-airmixture device according to claim 1, wherein said apertured vaporisationblock is laid up from a plurality of layers, preferably by winding, saidlayers having regular formations extending out from each layer to spaceit from said next layer.
 10. A fuel-air mixture device according toclaim 9, wherein said formations at each layer are continuous with saidformations at the next.
 11. A fuel-air mixture device according to claim9, wherein said formations at each layer are inter-spaced with saidformations at the next.
 12. A fuel-air mixture device according to claim1, wherein said apertured vaporisation block is provided whollydownstream of the position of said fuel introduction means.
 13. Afuel-air mixture device according to claim 12, wherein an upstream faceof said apertured vaporisation block is concavely formed, preferablyconically.
 14. A fuel-air mixture device according to claim 1, whereinsaid apertured vaporisation block is provided at and extendingdownstream of the position of said variable orifice nozzle.
 15. Afuel-air mixture device according to claim 1, wherein said aperturedvaporisation block has at least one transverse bore leading from saidsecondary air passage to a respective one of said air passagewaysthrough said block.
 16. A fuel-air mixture device according to claim 15,wherein each of said passageways has a transverse bore leading from saidsecondary air passage.
 17. A fuel-air mixture device according to claim15, wherein some of said air passageways are not in communication withsaid secondary air passage, whereby they do not receive fuel-air mixturein use.
 18. A fuel-air mixture device according to claim 15, whereinsome of said air passageways are in communication with said secondaryair passage only via others of them.
 19. A fuel-air mixture deviceaccording to claim 14, wherein said fuel introduction needle extendsinto one or more of said air passageways in said apertured vaporisationblock.
 20. A fuel-air mixture device according to claim 15, wherein saidpassageway or each said passageway having said transverse bore or eachsaid bore is configured as a venturi with said narrowest throat being atsaid orifice(s) of said transverse bore.
 21. A fuel-air mixture deviceaccording to claim 15, wherein said passageway(s) have turbulenceinducing formations downstream of said transverse bore(s), to aidmixture of the fuel with the air in said passageways.
 22. A fuel-airmixture device according to claim 1, wherein said needle actuator isaccommodated in a fuel tight manner in a needle carrier and extends intoa lubricant chamber where said cam plate acts on it.
 23. A fuel-airmixture device according to claim 22, wherein said needle is carriedaxially of said needle actuator and spring biased towards said primaryair passage for closure of a fuel outlet orifice from said needlecarrier to said primary air passage by engagement of a taper of saidneedle in said orifice.
 24. A fuel-air mixture device according to claim23, wherein said needle carries an O-ring arranged to seal additionallysaid orifice with said needle.
 25. A fuel-air mixture device accordingto claim 22, wherein said needle carrier has an extension incommunication with said primary air passage and said extension has twooutlets from said secondary air passage into said extension.
 26. Afuel-air mixture device according to claim 25, wherein one of saidoutlets is from a slow running branch of said secondary air passage,having a slow running air flow adjustment and a second branch which isnormally open, except when closed by a closure valve on closure of saidthrottle.
 27. A fuel-air mixture device according to claim 26, whereinsaid closure valve comprises a flat on a shaft of said throttle, whichis arranged to open said branch when said throttle is open.